This invention relates to a method of increasing the capacitance of anodized aluminum anode foils.
In Japanese Patent 55-69291, a method is disclosed of increasing the capacitance of an anodized aluminum foil by treating the foil before anodization with an organic solvent solution of a metal alkoxide such as titanium methoxide, hydrolyzing the resultant layer of metal oxide by treatment with boiling water, heating this treated layer and anodizing the thus treated layer. As a result the aluminum foil is covered with a layer of titanium dioxide.
A similar method is disclosed in Japanese Patent 80-69291. In this patent use of additional alkoxides of titanium including the isopropoxide is disclosed.
Japanese Patent 60-115215 discloses a method of first anodizing an aluminum foil then coating the anodized aluminum foil with an alcohol solution containing a metal alkoxide such as titanium isopropoxide, then thermally decomposing the coating.
A serious problem with the use of the methods of these references is that these methods require the use of a totally non-aqueous environment. Even the small amount of water that may be present in atmospheric humidity can destroy the alkoxide solutions employed. Such water-free conditions are very difficult to establish and maintain during the continuous production required for the large scale manufacture of the aluminum foils.
It has been found that the adhesion of the oxides such as titanium oxides made by the method of these references to the aluminum foil is not sufficient to prevent lift-off during the forming operation unless extraordinary care is employed.
Additionally, these references do not indicate whether the methods disclosed are applicable to etched aluminum foils.
British Patent 2041647 shows a method of doping a foil before formation or after formation with titanium by use of ion implantation. However, there is no suggestion that the titanium is oxidized so as to form titanium oxide. Additionally, this method is too slow to substantially raise the capacitance of the foil. Further, this method is not applicable to etched foils.